Dual polarized horn



March 9, 1965 Filed Jan. 28, 1960 C. T. CARSON DUAL POLARIZED HORN 2Sheets-Sheet 1 March 9, 1965 c. T. CARSON 3,173,146

DUAL POLARIZED HORN Filed Jan. 28, 1960 2 Sheets-Sheet 2 United StatesPatent 3,173,146 DUAL IQLARIZED HGRN Cyril T. Carson, Philadelphia, Pa.,assignor, by mesne assignments, to Washington Aluminum (10., Inc.,Baitimore, Md., a corporation of Delaware Filed Jan. 28, 1960, Ser. No.5,279 Claims. (Cl. 343-786) This invention relates generally to dualpolarized horns, apertures and the like, and more particularly relatesto novel horns with equal E and H plane radiation patterns.

In a dual polarized horn, two independent microwave signals areutilized, polarized at 90 in space orientation to each other so as to bemutually non-interfering. Such signals may both be either transmitted orreceived by the horn; or one transmitted, while the other is received. Atypical range of application of the invention is between 300 and 3000megacycles, though it is useful beyond such range. The horn hereof mayfor example be used in a large scatter-type antenna communicationsystem, for simultaneous transmit and receive with 90 difference inpolarization of signals; or in a radar system transmitting circularpolarized waves, and receiving reflections thereof. Such simultaneousutilization of the dual horn enhances the practicableness of thesystems.

A horn, to be effective in dual polarization operation, should havesubstantially identical E and H plane patterns. Heretofore thin metallicsepta were inserted cen trally along the horn interior walls to affectthe E plane pattern. The septa had negligible effect on the H planepattern. In accordance with the present invention novel means of patterncontrol are incorporated in the dual horn, affording more uniformattenuation of the E pattern skirts. The resultant horn characteristicsbetter match the impedance of the attached wave guide or its airloading, thus having far better VSWR than heretofore attainable.

Metal fillets or inserts are applied along the corners of the basichorn. These fillets are suitably tapered along the horn flare. Thelength of the fillets may be as low as one quarter wave length or even awave length or more (of the signal frequencies of the horn operation).The cross-sectional shape of the fillets or corner inserts may take anumber of forms, as will be set forth. The crosssectional size and formof the fillets may be varied, and optimized empirically for a particularhorn.

The invention inserts may be applied to horns of various sectionalconfigurations, e.g. square, rectangular, circular. It is preferablethat the horn be at least one wave length long, with the insertspreferably of the order of one half wave long. Substantial impedancematching is accomplished by the invention born, with VSWR of the orderof 1.15. Sepia pattern control results in VSWR in the range of 1.5 to 2.The corner fillets hereof changes the E plane up to about 30, and the Hplane only a few degrees, as will be detailed hereinafter. Moreeffective pattern control is thereby provided.

It is accordingly a primary object of the present invention to provide anovel dual polarization born with substantially equal E and H planepatterns.

Another object of this present invention is to provide a novel horn withcorner inserts or fillets effecting pattern control.

A further object of this present invention is to provide a novel dualpolarization horn matched to its associated guide or load with VSWR ofthe order of 1.15.

Still another object of this present invention is to provide a novelhorn the relative E and H patterns of which are effectively controlledby simple tapered fillets.

These and other objects of the invention will become 3,173,146 PatentedMar. 9, 1965 more apparent in the following description of exemplaryembodiments thereof, illustrated in the drawings in which:

FIGURE 1 is a perspective illustration of one form of the invention dualpolarized horn.

FIGURES 2, 3 and 4 are perspective views of several forms of taperedcorner fillets for the horn of FIGURE 1.

FIGURES 5, 6 and 7 are end views of various corner fillets transverseforms.

FIGURES 8, 9 and 10 are cross-sectional views through modified filletshapes.

FIGURE 11 is a transverse sectional view at an end region of a furtherhorn embodying the invention.

FIGURE 12 is a diagram illustrating the invention applied to anexponential horn.

FIGURES 13 and 14 are diagrams used in explaining some technical aspectsof the invention.

FIGURES 15 and 16 are graphs of E and H patterns showing their controlby the invention inserts.

FIGURE 1 illustrates in perspective a horn 20 simultaneously operablewith two non-interfering micro-wave signals, polarized at 90 spatialorientation. Horn 20 is rectangular in section with its throat 21connected to a wave guide 22 indicated in dotted lines. The hornaperture 23 may radiate to (or receive from) open space, a lens orreflector. The four walls 24, 24 taper outwardly from throat 21 toaperture 23. At each interior corner of the horn are metallic inserts orfillets 25, 25. The conductive fillets 25, 25 are tapered, and flare outwith the horn. Also fillets 25, 25 extend the full length of horn 20,although such is not necessary as will be explained hereinafter.

FIGURE 2 illustrates one of the fillets 25 with respect to the linearcorner 26 along the horn walls 24, 24. The aperture face 27 of fillet 25is substantially square though not necessarily, corresponding to thesquare sections 21, 23 of the horn 20. The throat face 28 is correspondingly square in form, though smaller in area than face 27. The twotrapezoidal sides 29, 30 are simple and relatively inexpensive toconstruct.

The corner fillets may be of flat or sheet material, with hollowinteriors. The faces 27, 28 may be metallic planes or open as desired.The significant factor is that the longitudinal surfaces (29, 30) be ofgood conductive material to effect the pattern control. Also, thetapering of the corner fillets 25 may take many alternate forms, withgood pattern control.

FIGURE 3 shows the face 27' tapered to a line 31 at throat 21 to formcorner fillet 35 with triangular side 32 and trapezoidal Side 33. FIGURE4 shows corner fillet tapered from square face 27" to a point 36, withtwo triangular faces 37, 38. It is noted that the longitudinal faces ofthe corner fillets 25, 35, 40 are plane. Plane faces are more economicalthan curved ones; the latter may be used as well.

The end faces of the fillets may be square, rectangular, or any otherdesired shape. Where flat sides are used, the horn aperture face 41,shown in FIGURE 5 is square; face 42 is rectangular, with the longerside 43 horizontal, as shown in FIGURE 6. FIGURE 7 shows face 44 with avertical longer side 45. The interior corners 46, 47 of fillet faces 41,42 respectively, are sharp or squared, corner 48 of fillet face 44 beingrounded. The first order dimensioning of the fillet shape is discussedin more detail hereinafter in connection with FIGURE 13.

The cross-sectional form of the corner inserts or fillets may be varied.In FIGURE 8 a single plane 50 subtends perpendicular horn walls 51, 52,being inclined therebetween at a desired angle. The interior portion 53may be hollow or solid. The interior surface 55 of FIGURE 9 between hornwalls 56, 57 is arcuate; being a 90 circular section. The fillet section60 of FIG- 3 URE is a full circle or tueb tangent at 61, 62 respectivelyto walls 63, 64.

The important factors of the fillets hereof is that their surfacesinterior of the horn be of material of good conductivity, such asaluminum, that there be good electrical contact between the edges ofthese surfaces and the metal horn walls they subtend. The waves passingalong the horn are short circuited at the fillet areas, withshort-circuiting currents flowing across the fillet surfaces to theadjacent horn walls, as will be set forth in more detail in connectionwith FIGURE 14. A given horn will generally, though not necessarily, beprovided with fillets of the same form, construction, and length. Also,a particular horn may use only two fillets, generally diagonallyarranged.

Horns are generally at least one-half wave length long; usually a fullwave length, or longer. The horn 70 of FIGURE 11 is shown to be one wavelength A long; and may of course be even longer (or shorter). The cornerfillets 71, 71 of horn 70 are one-half wave length long, M2. The filletsmay be shorter, such as even to one-quarter wave length, M4, or less; orlonger, to one wave length A or more. Their length is not critical. Inpractice, a length of one-half. the wave length of the horn designcenter frequency is most economical for eifective results. There is nofrequency discrimination produced by the corner fillets, hence the broadband characteristic of the horn is unimpaired. The shorter fillets 71,71 preferably, though not necessarily, extend to the aperture 73 of thehorn.

The E and H plane pattern control by the corner inserts hereof is alsoequally operative on exponential horns. Horn 80 of FIGURE 12 is of suchtype. The fillets 81,: 81 are in the corners of horn 80 if of square orrectangular form. They are one-half wave length long in horn 80. Theinterior surfaces 82, 82 of fillets 81, 81 are shown as curved. They maybe flat for reasons of economy, as are the corresponding surfaces 72, 72of horn 70. Where conical or other round, horn shapes are used, thefillets therefor are located in the effective corners thereof,corresponding to the 45 points between the 90 orientations of the twosignals through the horn.

The cross-sectional area of the corner fillets are best arrived atexperimentally or empirically. The larger the area of the filletsextending into the horn interior, the greater the effect on the E-Hpatterns. The born 85 of FIGURE 13 has a rectangular aperture with fourcorner fillets 86, 86. tangular with dimensions a, b. The a width of thefillet faces corresponds to the A dimension of the horn aperture; the bheight, to the B dimension. As a first order approach the ratio of a tob is chosen as that of A to B. However, the desired pattern control fora given horn is then best trimmed empirically, and optimized ifrequired.

Each corner fillet in a horn of the invention affects the surrounding Eplane substantially more than the H plane. The E plane pattern may bechanged up to while the H plane pattern, onlya few degrees. The filletsshort out parts of the horn aperture, controllably distorting both the Eand H plane patterns simultaneously. The extent of such distortioncorresponds to the surface area intercepted by the waves passingthrough. The short circuiting'currents flow across the fillet surfacesand around the subtended horn corners.

FIGURE 14 is a graphic representation of the physical action of born 90with corner fillets 91,91. The E field through the horn is verticallyoriented for one of the signals. The horizontal lines s, s divide thehorn area into equal segments of arbitrary number. The integration ofthe field intensity E across each segment results in an equal amount ofenergy in each segment. The fillets 91, 91 short circuits the electricfields Eat the corners, and blocks out the magnetic fields H therein aswell. The

The faces of' fillets 86, 86 are recresultant intensity distributionacross the horn is indicated by smooth curve 92. A similar smoothingaction occurs on the transverse E pattern for the second signal. Therespective magnetic H patterns are correspondingly affected, to a lesserdegree.

FIGURE 15 is a radiation pattern of the E and H planes (in solid lines)of a typical horn configuration, unaltered by corner fillets, septa,etc. The objective of E, H plane pattern control hereof is to alter thebasic E and H plane patterns so that they more closely coincide, withleast VSWR impact. The corner fillets of the present invention widenboth 90 signal E plane radiation patterns, and effectively remove theirwide angle radiations. As viewed in FIGURE 15, the result is to widenthe E plane patterns to coincide with H plane patterns and give lowskirt levels as shown in dotted curve F. To a lesser extent, the sidesof the H pattern are trimmed to coincide with the resultant E planepattern per curve F. v

The polar radiation pattern (hatched area) of FIG- URE 16 isillustrative of the E plane radiation altered by corner fillets in thehorn in accordance with this invention as compared with the pattern 101obtained using septa. This is readily accomplished by the inventionconductive inserts, with a residual VSWR of the order of 1.15.

The use of the corner fillets permit an overall better impedancematching of the horn to either or both ends thereof, as aforesaid. Theresultant E and H radiation patterns are made substantially equalthereby, for efiective operation of the horn, with dual polarization. Byeffective design following the principles of this invention, the E and Hradiation patterns are made substantially equal thereby, for effectiveoperation of the horn with dual polarization. By effective designfollowing the principles of this invention, the E and H radiationpatterns in both 90 signal orientations are similarly controlled forefficient results. Also, some or all of the metal inserts may be locatedaway from the corners, to provide effective action, on the E/H patternratio.

One practical embodiment of this invention, as a feed horn in atropo-scatter communication system, had the following physical andelectrical characteristics:

Aperture: 15" x 13.5" Length: 40" Throat: 11.75" x 11.75" Centerfrequencies:

Polarization A: 777 me. (1:15.2) Polarization B: 857 me. (1:13.75")Fillet dimensions (one in each corner):

Length: 12" 'I-Ieight at aperture: 3% Width at aperture: 278" Height atinterior end: Zero Width at interior end: 2%" VSWR=L10 for both A and Bsignals. 10 db beam width without fillets: E plane at 777 mc.: 98 Hplane at 777 mc.: 112 E plane at 857 mc.: 76 H plane at 857 mc.: 109 10db beam width with fillets: E plane at 777 mc.: 107 H plane at 777 mc.:104 E plane at 857 mc.: 105 H plane at 857 mc.: 104

Although this invention has been described in connection with exemplaryembodiments thereof, it is to be understood that variations andmodifications may be made by those skilled in the art that fall withinthe broader spirit and scope of the invention as set forth in theappended claims.

What is claimed is:

1. A dual polarized horn of the character described comprising a flaredstructure having walls joined at corner regions and conductive meanssecured to adjacent ones of said wall surfaces, at said corner regions,interior or" the walls and longitudinally of the horn for substantiallynarrowing the radiation pattern in the E-plane with relatively low VSWReffect, each of said conductive means being a plane triangular sheet ofconductive material being positioned to form a pyramidal shell with itsassociated corner region, and substantially confined to the intersectionof the adjacent wall surfaces at its respective corner region.

2. A dual polarized horn of the character described comprising a flaredstructure having walls joined at corner regions and conductive meanssecured along the corner regions interior of the walls andlongitudinally of the horn for substantially narrowing the radiationpattern in the E-plane with relatively low VSWR effect, each of saidconductive means being a plane triangular sheet of conductive materialbeing positioned to form a pyramidal shell with its associated cornerregion, said pyramidal shell being tapered to narrow in the directionfrom the aperture towards the throat of said horn.

3. A dual polarized horn of the character described comprising a flaredstructure having walls joined at corner regions and conductive meanssecured along the corner regions interior of the walls andlongitudinally of the horn for substantially narrowing the radiationpattern in the E-plane with relatively low VSWR efiect, each of saidconductive means being a curved sheet of conductive material beingpositioned to form a prismoidal shaped shell with its associated cornerregion, said shell having a taper running from the aperture to thethroat of said horn.

4. A dual polarized horn of the character described comprising a flaredstructure having walls joined at corner regions and conductive meanssecured to adjacent ones of said wall surfaces, at said corner regions,interior of the walls and longitudinally of the horn for substantiallynarrowing the radiation pattern in the E-plane with relatively low VSWReffect, each of said conductive means being a substantially L-shapedsheet of conductive material being positioned to form a rectangularshell with its associated corner region, and substantially confined tothe intersection of the adjacent wall surfaces at its respective cornerregion, said rectangular shell having a taper running from the apertureto the throat of said horn, narrowing towards the throat of said horn.

5. A dual polarized horn of the character described comprising a flaredstructure having walls joined at corner regions and conductive meanssecured along the corner regions interior of the walls andlongitudinally of the horn for substantially narrowing the radiationpattern in the E-piane with relatively low VSWR efiect, each of saidconductive means being a plane triangular sheet of conductive materialbeing positioned to form a pyramidal shell with its associated cornerregion, the length of said shell being substantially equal to one-halfwave length of the mean frequency of the horn signals.

References Cited by the Examiner UNITED STATES PATENTS 2,317,464 4/43Katzin 343786 2,712,067 6/55 Kock 343-783 2,994,084 7/61 Miller 343-7833,096,519 7/63 Martin 343756 FOREIGN PATENTS 715,957 9/54 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

1. A DUAL POLARIZED HORN OF THE CHARACTER DESCRIBED COMPRISING A FLAREDSTRUCTURE HAVING WALLS JOINED AT CORNER REGIONS AND CONDUCTIVE MEANSSECURED TO ADJACENT ONES OF SAID WALL SURFACES, AT SAID CORNER REGIONS,INTERIOR OF THE WALLS AND LONGITUDINALLY OF THE HORN FOR SUBSTANTIALLYNARROWING THE RADIATION PATTERN IN THE E-PLANE WITH RELATIVELY LOW VSWREFFECT, EACH OF SAID CONDUCTIVE MATERIAL BEING A PLANE TRIANGULAR SHEETOF CONDUCTIVE MATERIAL BEING POSITIONED TO FORM A PYRAMIDAL SHELL WITHITS ASSOCIATED CORNER REGION, AND SUBSTANTIALLY CONFINED TO THEINTERSECTION OF THE ADJACENT WALL SURFACES AT ITS RESPECTIVE CORNERREGION.